In recent years, with mankind's increasing and continuous reliance upon hydrocarbon fuels and products, and the depletion of existing oil fields on land in the western hemisphere, extensive and costly efforts have been made to locate petroleum deposits that underly the floors of various large bodies of water such as lakes, seas and oceans. In North America, substantial oil and gas well drilling activity has taken place in the Beaufort Sea, which is in the Arctic Ocean north of Alaska and the northern territories of Canada. Petroleum geologists generally believe that several of the sedimentary geological formations located below the floor of the Beaufort Sea contain large deposits of petroleum material.
Being in a polar region, drilling oil and gas wells in the Beaufort Sea is a hazardous and expensive operation. Ambient temperatures are extremely low during the wintertime. Moreover, tremendous pressures are generated against the drilling station by polar ice. One of the methods used in the Beaufort Sea in preparation for drilling an oil well is to build an artificial island at the location where the well is to be drilled. The material for such islands is dredged from the sea floor and piled in one location until the surface of the island is above the water and ice level. Substantial effort to date has been concentrated in the Canadian sector of the Beaufort Sea where the exploration procedure has followed two main patterns. In relatively shallow water, up to about 19 meters, drilling has been a winter operation from artificial sand islands formed the previous summer by dredging and dumping from barges. In deeper water, from 25 to 68 meters, drilling has been a summer operation using drill ships.
Sand deposited under water tends to take up a very flat edge slope of about 7 to 8 percent with the result that artificial islands in water deeper than about 10 meters consume huge quantities of sand and are hence very expensive to construct. In order to overcome this problem, a caisson-retained island has been developed whereby the upper portion of the sand is retained by a ring or collar of caissons. These are founded on an underwater pad of dredged sand about 10 meters below sea level. Dome Petroleum, a large Canadian company which is actively searching for oil in the Beaufort Sea, completed a concrete caisson-retained island in the fall of 1981. Esso Resources is presently proceeding with the construction of a tensioned steel caisson retained island.
Numerous procedures and apparatus for drilling oil wells in the formations below water bodies have been proposed. Some of these procedures and apparatus are disclosed in the patents listed below:
______________________________________ Patent No. Issue Date Inventor ______________________________________ U.S. 2,472,869 June 14, 1949 Travers 2,589,153 March 11, 1952 Smith 2,939,290 June 7, 1960 Crake 2,973,046 Feb. 28, 1961 McLean 4,037,424 July 26, 1977 Anders 4,080,798 March 28, 1978 Reusswig et al. 4,118,941 Oct. 10, 1978 Bruce Cdn. 470,212 Dec. 19, 1950 Travers 966,320 April 22, 1975 Guy 971,758 July 29, 1975 Best 1,063,817 Oct. 9, 1979 Cashman 1,066,900 Nov. 27, 1979 Bennett ______________________________________
The basic theme of most of these references is to provide artificial islands or operation sites in water bodies such as the Beaufort Sea or the Gulf of Mexico for the purpose of supporting equipment such as drilling rigs engaged in searching for petroleum deposits below the water body floor. Current techniques for building islands cost in the hundreds of millions of dollars and usually consist in part of dredging solid matter from the water body floor and heaping it to thereby provide a foundation of earth material upon which can be situated various types of hardware such as submerged barges or caissons, the tops of which ultimately penetrate the surface of the water body. In some cases, to reduce slump, the sides of the island are supported with a retaining member such as a wall or caisson.